Overload devices



May 24, 1960 G. M. SOMMER 2,937,734

OOOOOOOOOOOOO ES INVENTOR:

GORDON M. SOMMER ATT'YS May 24, 1960 G. M. SOMMER OVERLOAD msvxcas 4 Sheets-Sheet 25 Filed July l6 1957 GORDON M. SOMMER WW, -*S" May 24, 1960 e. M. SOMMER OVERLOAD DEVICES 4 Sheetsheet 4 Filed July 16, 1957 FIG.7

FIG. 8

'IIIL I2 INVENTOR. GORDON M. SOMMER ATT'YS United Stat es Patent O OVERLOAD DEVICES Gordon M. Sommer, I-Iinsdale, 111., assignor Industries, Inc., New York, N.Y. a corporation of Delaware Filed Ju!y 16, 1951, Ser. N0. 572,230 y 2 Claims. (C1. 192-150 This invention relates :to overload devices and more particularly to overload devices which are particularly well adapted for use in metal-wonking presses, and the:

like.

A primary object of my invention is to aflford a novei overload device which 1's operable to prevent stalling; and breakage of a press when the press load exceeds apredetermined amount.

It is not unusual for a metal-working press fcoibe overloaided during the working stfoke because of improperly set dies, the feeding of two work pieces to the press, in

stead of one, and the like. When this occurs, the press may be broken, or the clutch may slip, causing the pressto Stall at (the bottom of its stroke. When breakage occurs, not only are costly repairs incurred, but also a costly delay in production may result for the time necessary to effect repairs. When the press stalls, it becomes nccessary to efiect time-consuming repairs so as to relieve the stalled condition.

It is an object of my invehtion to afford a novel ovefload device which is efiective to prevent such br eakage or stallingof a press. w

Another object is to aiford an overload device of the aforementioned ype which acts automatically to stop the press when the press load exceeds a predetermined Yet' another Object of my invention is to aiford a novel and practical overload device which is etfective and efli- 50 cient in operation, and which inay be readily and economically produced commercially.

Other and dfu1ther objects of the present invention will i be apparent from the following description and claims and ard illustrated in the accompanying drawings which, by way of illustration, show a preferred embodiment of the present invention and the principles thereof and what I now considerto be the best mode in which I have coutemplated applying these principles. Other embodiments of the invention embodying the sarne 01' equivalent principles may be used and struetural changes may be made as desired by those skilled in the art without departing from the present invention and the purview of the ap pended claims.

In the drawings:

Fig. 1 is a freut elevational view of a press embodying overload-* devices embodying the principles of my im vention;

-Fig. 2is an enlarged detail sectional View taken substantially along the line 22 in Fig. 1;

Fig. 4 is a detail sectional view taken substantially along the line 4-4 in Fig. 2;

Fig. 5 is a detail sectional v-iew taken substantially along the line 55 in Fig. 2;

Fig. 6 is an enlarged detail sectional view of a portion of the press shown in Fig. 3;

Fig. 7 is a fragmentary sectional view cf a press showing my novel overload device unit s mounted'in operative position in the lower die thereof;

Fig. 8 is a fragmentary sectional view somewhat similar to Fig. 7, but showing my novel overload device units monted in the bolster of a press; and

Fig. 9 is a fragtnentary sectional view somewhat similar to Fig. 8, but sho'wing my novel overload device units mounted in the upper die 01' punch of a press.

A metal-working press P'embodying my novel overload device is showh in Figs. l to 6, inclusive, of the drawings, to illustrate the preferred embodiment of my invention.

The pre'ss P, illustrated in the drawings, is a mechanical type, which is Operated by means of cranks or eccentrics to reciprocate the slide or slides therein. The gen eral const-ruction and arrangement in the press is well Fig. 3 is a detail sectional view take11 substanti.ally

known to those skilled in the art and -includes in general,

a bed 20 at the lower end thereof, a crown 22 at the upper end thereof, and uprights 24 and 25 at the opposite sides of the press which separate the crown 22 from the bed 20. These parts constitute the press frame and each of the uprights 24 and 25 is 'provided with a guideway 27 for the purpose of guiding a substantially rectangularshaped slide 29 in its reciprocating movement toward and away from the bed 20. The slide 29 is mounted at each of its four corners 011 the lower end portion of a respective one of four vertically extending adjusting screws 3 1, only two of which are shown in the drawings, Fig. 1, eachof the four screws 31 being connected to a respective one of the corners cf the slide 29 in a manner which will be discussed in greater detail presently. The adjusting screws 31 are caused 10 simultaneously reciprocate in a vertical direction by a suitable and weil 'known mechanism, and it is this reciprocation of the screws 3 1 that causes the slide 29 to be moved upwardly and downwardly along the guideways 27 toward and away -from the lower die, not shown, which would be mounted on the.

bolster 34 on the bed 20.

The slide actuating mechanism of the press P is oper' ated by a motor 36, which drives a gear train by means of a pulley 37 on the motor shaft, one or more belts 39, and a driving wheel 41. The particular type of mechanism operating the slide may be any one of a number of specific forms, all well known in the art, and it need not be specifically' described herein inasmuch at it forms no part of the invention. It is suflicient to point out that the mechanism reciprocating the adjusting screws 31 also reciprocates the slide 29 toward and away from the bed 20. The bed 20 and slide 29 may each have a die mounted thereon so that when the two dies come together, a sheet of metal may be stamped into a predetermined form.

The substantially rectangul-ar-shaped slide 29 has two 44 has two spaced openings 51 formed therein, Figs. 1

and 3, and each of the adjusting screws 31 extend through a respective one of the opern'rrgs 51. Four housings 53,

which are identical in construction, are mounted on the plates 43 and 44, the housings 53 mounted on the plate 43 being disposed around respective ones of the adjus t-j ing screws 31 at the left end of the press P, as viewedf in Fig.1andthe housings 53 mounted on the Plate Patented May 24, 1960 44 being disposed around respective ones of the adiusting screws 31 at the right end of the press P, as vwwed in Fi 1.

Ea:h of the housings 53 embodies a bottom wall 55 having four outwardly projecting flanges 57 spaced therearound, Figs. 1 and 2 and each of the housings 53 is secured to the respective one of the plates 43 o1- 44 011 which it rests by bolts 58 projectin g through the flanges 57 and the respective plate 43 or 44. A substantially cylindrical-shaped side wall 59 projects upwardly from the bottom wall 55 ot each housing 53, and a top wall or cover 61 is mounted on the upper edges of the side wall 59. Four bolts 63 extend through bosses 66, projecting outwardly from the side wall 59 and bosses 65, correspondingly positioned 011 the cover rnember 61, and the cover member 61 is secured to the side wall 59 by nuts 67 threaded onto the bolts 63, Figs. 2, 3 and 4.

Bach of the adjusting screws 31 has a nut. 71mounted thereon and threadedly engaged therewith, Figs. 1 and 3. Bach nut has a flange 73 projecting horizontally ontwardly to thereby afiord a horizontally extending upper shoulcler 73a and a horizontally extending lower shoulder 73b. The top wall 61 of each housing 53 has a horizoutally disposed inwardly projecting shoulder 61a, which is normally disposed.in juxtaposition to the uppe'r shoulder 73a on a respective one of the nuts 71, Fig. 3. Bach nut 71 also has a reduced upper end portion 71a projccting upwardly from the shoulder 73a and journalled in the top wall 61. Bach nut 71 also has a reduced lower and portion 71b projecting downwardly from the shoulder 73b and extcnding through an annular-shapcd pressure ring 75, which extends around the lower end portion 71b in spaced relation thereto.

Bach housing 53 is substantially cylindrical in crossscction between the bottom wall 55 and the top wall 61, the side wall 59 defining a bore 60 having an upper end portion 60a of enlarged cross-scction and a. lower end portion 60b of reduced cross-section to thereby afiord an upwardly facing horizontally inwardly projecting shoulder 59a disposed between the upper and lower end portions 60a and 60b of the bare 60. The pressure ring 75 in each housing 53 is journalled in thelower end portion 60b of the respective housing 53 and is vertically slidable therein. Bach lower and portion 60b has five longitudinally extending, substantially arcuate-shaped reccsses 77 formed in the inner face thereof in equally spaced relation therearound, and five substantially cylindrical-shaped overload units 81 are mounted in upright position on the bottom wall 55 of the housing 53 in respective ones of the recesses 77 outwardly of the screw 31 on which the respective housing 53 is mounted, Figs. l, 2 and 3.

Each cf the overload units 81 embodies two substantia.lly cylindrical-shaped body members 83 and 84 disposed in longitudinal alignment with each other, Figs. 1, 3 and 6. Each of the body members 83 and 84 has a radially outwardly projecting flange 83a and 84a, respectively, the flanges 83a and 84a being forrned on the outwardly disposed ends of the body mcmbers 83 and 84. The upper body mernber 83 has an internally threaded bore 86, of uniform cross section, extending longitudinally therethrough. The lower body member 84 has a bore 87 extending longitudinally therethrough, the uppcr or inner end portion 87a of the bore 87 being of the same cross sectional size as the bore 86, and the lowcr or outer and portion 87b of the bore 87 being of enlarged cross sectional size to thereby form a downwardly facing, inwardly projecting shoulder 89 betwecn the end portions 87a and 87b.

An elongated rod 91 having a substantially cylindrica'l s'uaped shank 93, which has threads formed on 0116 end portion 93a thereof and an enlarged head 93b formed on the other end thereof, is slidably mountcd in the borc 87, with the head 93b disposed below the shouldsr 89. The endportion 93a cf the rod 91 is threadedly engaged in the bore 86 in the body member 83, and the enlarged head 93b is normally disposed in abutting engagement with the shoulder 89 of the lower body rnember 84 as shown in Fig. 6.

A plurality of annular-shapcd disc springs 95 are mounted 011 the body members 83 and 84 in encircling relation thereto. Bach disc 95 is formed of spring steel and is so shaped as to be concave in cross section on one face 95a thereof and convex in cross section on the opposite face 95b thereof, Fig. 6. The discs 95 are disposed in stacked relation around the body members 83 and 84 between the fiangcs 83a and 84a, with the ontwardly disposed faces of the discs 95 at the ends of the stack disposed in juxtaposition to the immer face of the flanges 83a and 84a, respectively. In forming the stack of discs 95, I prefcr to have the discs stacked in alternate pairs of convex and concave discs. That is, for example, with twelve discs mounted bctween the flanges 83 and 84 as shown in Fig. 6, the bottom two discs would be canvex downwardly, the next two discs would be convex upwardly, the next two discs would be concave downwardly, and so on until the top two discs are convex upwardly, so that at each end of the stack, the flanges 83a and 84a, respeclrively, are engaged with normally outwardly bulging central portions of adjacent discs 95. How ever, as will be apprcciated by those skilled in the art, the alternating of concave and convex discs may be 0therwise arranged such. as, for example, having adjacent individual discs alternately concave and convex, or the like, withoutdeparting from the purview of nur invention.

The rod 91 is longitudinally slidable in the bore 87 in the body member 84 and the disc springs are disposed in such position between the flanges 83a and 84a as to normally hold the head 93b of the rod 91 in abutting ehgagement with the flange 89 formed in the bore 87 in the lower body member 84, with the inner ends of the body members 83 and 84 disposed in spaced relation to each other.

The overload units 81 are mounted in each housing 53 with the lower faces 84b of the body rnembers 84 resting on the upper face of the bottom wall 55 of the housing 53, Fig. 3. The pressure ring 75 in the respective housing 53 rests on the upper face 83b of the body members 83 therein. The pressure ring 75 is attached to the overload units 81 by bolts 97, the lower ends oi'. which are threaded into the upper end portions of the rods 91, the upper ends of which are threaded into the ring 75, Fig. 3. In assembling the press1ire rings 75 and the overload units 81 in each housing 53, the bolts 97 may first be screwed into the overload units 81. The bolts on the overload units 81 may then be screwed into the respective rings 75. 'I'he rings 75, with the respective overload units 81 thus attached thereto may then b: dropped downwardly, as a unit, into operative position in the respective housings 53 before the latter are mounted on the screws 31.

A substantially annular-shaped warm gear 101 is slidably mounted on the flange 73 of each nut 71 for axia.l sliding movement relative thereto, and is non-rotatably secured to the nut 71 by suitable means such as a key 103, Fig. 3. Bach worm gear 101 rests 011 the shoulder 59a of a respective housing 53, and the upper edgc of the worm gear 101 is disposed in abutting engagement W1th the shoulder 61a on the cover member 61 of that housing 53, radially outwardly of the nut 71 A wenn 105 is journalled in an outwardly projecting portion 53a cf each respective housing 53, Figs. 2 and 3, and is operatively engaged with the wenn gear 101 therein. It will he Seen that upon rotation of each worm 105, the worrn gear 101 and therefore the nut 71, Will be caused to rotate around the adjusting screw 31 on which it is mounted to thereby move the nut 71 longitudinally along the adjusting screw 31. Such movement of each nut 71 longitudinally upwardly a.long the adjusting scrcw 31 i:-

ffective to raise the housing 53 and, therefore, that Corner of the slide 29 in which thescrew 31 is mounted. Likewise, downward movement of the nuts 71 longitudinally of the adjusting screws 31 in effective to lower the housing 53 and that corner of the slide 29 in which the respective adjusting screw 31 is mounted, so long as the slide 29 is free to be thus moved downwardly.

Four switches 97 of a suitable type, such as, for example, micro-switches, are mounted 011 the covers 61 of the fonr housings 53, respectively, Figs. 1, 2 and 5. Bach switch 97 embodies a housing 97a from which an elongated switch arm 97b projects, and the housing 97a thereof is mounted on a respective one of the covers 61 in such position that the free end of the arm 97b rests 011 the upper end of the adjacent nut 71 and is held thereby in on or closed position, when the mit 71 is disposed in normal position in its housing 53 With the shoulder 73a disposed in engagement With the shoulder 61a. The arm 97b is preferably spring urged in a counter clockwise direction toward o or open position as viewed in Fig. 5. Bach of the switches 97 may be connected in series into the power circuit for the motor 36 so that, when the switches 97 are closed they are ineffective to stop the motor 36. When, under overload conditions in the press P, as will be discussed in greater detail presently, any one of the nuts 71 is moved downwardly, relative to its housing 53, a distance suflicient to permit the switch arm 97b resting thereon to rotate in the aforementioned counter clockwise direction into ofi position, the circuit to the motor 36 is thereby broken and the press P is thus automatically stopped.

In a press such as the press P shown in the drawings, wherein the slide 29 is mounted on four adjusting screws 31, each of the adjusting screws normally carries onefourth of. the load, for example, if the press? is a two hundred ton press, each of the adjusting screws 31 would carry one-fourth of the nominal load, or, in other Words, fifty tons. This, of course, would mean that With the arrangement shown in Figs. 1 to 6 of the drawings, wherein the pressure ring 75 in each of the housings 53 is supported by live overload units 81, each of the overload units 81 must be capable of transmitting a force of ten tons from the pressure ring 75 to the bottom Wall 55 of the housing 53 in normal opcration of the press P, preferably without permitting any relative movement between the nuts '71 and the slide 29. With my novel invention, the overload units 81 may be readily preloaded to accomplish this purpose. This may be accomplished by adjusting the rod 91 longitudinally in the threaded bore 86 in the body member 83 of each of the overload units 81 to such a position that the disc springs 95 are compressed to a point where the outward force on the body members 83 and 84 is the same as the force, such as, for example, the aforementioned ten tons, which it is desired that-they withstand without permitting relative movement of the nuts 71 and the housings 53. In actual practice, the overload units 81 normally will be preloaded to a point whereat the springs 95 exert a force equivalent to the proportionate share of the nominal force to be supported by the overload units 81 plus a permissible overload force such as, for example, 10 percent. Thus, under such conditions, in a press wherein the proportionate share of the nominal press load to be carried by each overload unit 81 would be ten tns, as set forth in the example above, each overload unit would be preloaded to ten tons plus percent, or eleven tons.

lt will be seen that With this construction, in the operation of the press P, when the slide 29 is normally moved down by the adjusting screws 31, the overload units 81 will not be compressed. However, if an overload condition is encountered which exceeds the preloading cf the overload units 81, the upper body member 83 and the rods 91 in each overload unit 81 will move axially downwardly relative to the lower body member 84 thereof. Thus, in the example set forth above, in a press nominall-y rated as a two hundred ton press Withth6' overload units 81 preloaded by tcn percent, the overload units 81 around any particular one of the screws 31 will remain in normal extended Position until the load an that particular screw exceeds the nominal load of fifty tons' plus the ten percent permissible overload condition of five tons, or, a total load of fifty-five tons. Theta after, as the force on thescrew 31 increases, the nut 71 and the pressure ring 75 will be moved downwardly, relative to the housing 53 and the worm gear 101, to thereby move the upper body members 83 of the overload units 81 around that particular screw 31 downwardly toward their respective body members 84. When the overload condition has proceeded to such an extent that the nut 71 on the particular screw 31 has moved downwardly away frorn the cover 61 on the housing 53 a stifiicient distance to perrnit the arm 97b an the rcspec tive switch 97 to rotate in a counter cloclcwise direction as viewed in Fig. 5, sufliciently to open the switch 97, the press P will be automatically stopped. 'I'his maximum overload condition may, of course, be set at any practical -desired amount, such as, for example, a fifty' percent overload condition above the nominal loading conditions. In such a case, the upper body menrbers 83 of the overload units 81 would be moving downwardly toward the lower body members 84 against the urging of the disc springs all the way from the ten percent' overload condition to the fifty percent overload condi{ tion, at which latter time the switch 97 would open to thereby stop the press P. An overload condition in ex cess of the maximum permissible overload condition occurring at any one of the screws 31 is elfective to corrx-' press the overload units 81 around that screw 31 a sufficient distance to open the switch 97 associated therewith and, thereby, stop the press P.

I have found it de-sirable to so construct the overload units 81 that the maxi-mum relative movement of the body membcrs 83 and 84 thcr-eof toward each other between preloaded condition and maximum overload con-' dition is approximately one-quarter of an inch.

It Will be seen that With the press P constructed in the manner shown in Figs. l to 6, inclusive, and With no press load being applied, the 'slide 29 is suspended from the nuts 71 on the four screws 31, the housings 53, to which the sl-ide 29 is attached by :the bolts 58, then being so disposed in such position on the nuts 71 that the shoulders 61a in the housings 53 rast on the shouldersf 73a on the nuts 71. Under these conditions, the Worms may be rotated in the proper directions to properly" rotate the respective worm gears 101 and nuts 71 in the housings 53 to adjust the nuts 71 and, therefore, the

slide 29 to proper positionon the screwS 31.

Thereafter, when the screws 31 are moved downwardly toward the bed 20, such as, for example,- When they are moved downwardly in a stamping operation, the housings, 53 and, therefore, the slide 29 move downwardly therewith so long as no overload condition -is kancountered bfy any corner of the slide 29 which is in exccss of the preload for that corner. When an overlo'ad condition in excess of such preloadis encountcred by'any corner of the slich3" 29, further downward movement of that corner a'nd the housing 53 thereon is stopped and ahy additional dowrzward movement of the screw 31 and nut 71 moves the pressure r-ing 75 and the upper body niembers 83 downwardly relative to that housing 53 and the lower body rnembers 84 of the overload units in that housing 53. If

such additional movement of that screw 31 is insuflicienf to compress the overload units an zimount sufficient to permit the switch 97 associated therewith -to ope'n,thr j press P is not stopped by my novel overload device. Tf,

on the othcr hand, such additional movement of the screw 31 is suflicient to compress the overload units an amount sufficient to open the switch 97 associated therewith, the press P is automatically stopped to thereby prevent further overloading thereof. The maximu-m overload im which my novcl device is set is such that the press P is automatieally stopped before the press is everloa ded to a point where it is broken, or where the slide 29 1's jammecl to an extcnt that it can not bc freed by merely backing 011 the actuating mechanism therefor.

I With rny novel invention, the overload device may be quickly and easily preloaded to the desired setting.

Also, it will be seen that my novel overload device units 81 may be readily placed in operative position in tlle press P.

In tl1e modified fo1m of my invention shown in Fig. 7. parls which are the same as parts shown in Figs. 1 to 6 are indicated by the Same refercnce numbers.

In Fig. 7, a die 201 is shown mounted on the bed 20 of a prcss P1. In the form of our invention shown in Fig. 7, tne overload units 81 are mounted in recesses 203 formed in 1he bottom of the die 201, With the upper cnds 83b of the units 81 disposed in juxtaposition to theinner ends of tl1e recesses 203, and With the lower cnds 84b disposed in juxtaposition to the upper face of the bed 20. The die 201 is slidably mounted on suitable tie down bolts 205 threaded into tne bed 20, and the supporting units 81 are of such length that the die 201 is normally supported thereby in upwardly spaced re1ation 10 the uppcr face of the bed 20.

The switch 97 is mounted on a suitable bracket 207 011 il1e bed 20 in such osition that the arm 97b of the switch 97 is normally engaged with a flange 209 projccting outwardly from the die 201 and is normally hold thereby in osition to maintain the switch 97 closed.

The supporting units 81 are preloaded to an extent wherein they are capable of normally holding the die 201 in the raiscd position relative 10 the bed 20 shown in Fig. 7. During tl1e operation of the press P1, shown in Fig. 7, when the overload condition becomes sufi1- ciently great that the ovcrload units 81 arc compressed in the manner heretofore discussed in greater detail with respect to my invention as shown in Figs. 1 to 6, indusivc, the flange 209 on the die 201 moves downwardly away from the arm 97b on the switch 97 a sufiicient distance to perrnit the switch 97 to open and thereby automzztically stop the prcss P1.

In the modified forn1 of my invention shown in Fig. 8, thc supporting units 31 are also mounted 011 the upper face of the bcd 20 of a press P2. However, in this form 01 our invention, the supporting units 81 are mounted in reccsses 303 formed in the bottom of a bolster 301 which is slidably mounted on suitable hold down bolts 305 projecting upwardly frorn the bed plate 20. Here again, the supporting units 81 are of such length that they norma1ly Support tl1e bolster 301 in raised position relative 10 the bed 20, and a switch 97 is mounted 011 a suitable brackct 307 or1 the bed 20 in such position that the arm 97b of the switch 97 is normally engaged with a flange 309 projecting outwardly from the bolster 301 in position to normally hold the switch 97 closed. When thc overload condition on the bolster 301 is sufi1cient to cause compression of the overload units 81 10 the maximum overload for which they are set. the flange 309 moves away from the arm 97b a suificient distance to perrnit the switch 97 to open und thereby automatically stop the press P2.

In the modified form of my invention shown in Fig. 9, thc overload units 81 are mounted in recesses 403 formed in the top of a punch 404 s1idably mounted on suitable hold down bolts 405 cxtending from an upper slide '29 slidably mounted in the guideways 27 of a press P3. T11e overload units 81 are of such length that thcy normally hold the punch 404 in downwardly spaced relation to the slide 29.

The switch 97 is mounted an a bracket 407 011 the slide 29' in such position that the arm 970 of the switch 97 is normally engaged with a flange 409 extending outwardly from the punch 404. When an overload condidition in the press P3 occurs which is sufficient to compress the overload units to a maximum amount, the punch 404 is moved upwardly toward the slide 29 a distance sufiicient to move the flange 409 away from the arm 97b suificiently to permit the switch 97 10 open and thereby automatically stop the press P3.

Frorn tl1e foregoing it Will be Seen that I have afiorded a novel overload device embodying novel overload units.

Also, it will be seen that I have aflorded a novel overload device wherein the overload units thereof may be readily incorporated in a wide variety 01 operative posi tions between actuated and actuating members, and be tween supported and supporting members in a metal working press, such as, for exarnple: between an adjusting nut and a slide actuated thereby; between a press bed and a die supported thereby; between a press bed and a bolster supported thereby; and between a slide and a punch or die supported thereby.

In addition, it will be Seen that I have afforded a novel overload device which is practical and eflicient in construction and in operation.

Thus, while I have illustrated and described the preferred embodiments of my invention, it is to be Understood that these are capable of variation and modification.

I claim:

1. An overload unit for use in a metal-working press having a Work-engaging mernber, and another member for moving said work-engaging member toward werkengaging position, said overload unit comprising two elongated and members disposed in longitudinal alignment with each other, each cf said elongated mcmbers having an enlarged head on the outwardly disposed end thereof, one of said elongated mem'oers being adapted 10 be supportingly engaged by said work-engaging mernber, and means normally holding said elongated members in longitudinally spaced relation 10 each other in position to be disposed in longitudinally extending position between such a work-engaging mernoer and such another member for movement by said last mentioned members longitudinally inwardly toward each other into an actuated position, said means comprising a rod slidably mounted in one of said elongated mernbers and threadedly engaged with the other of said elongated members, said one elongated member having a radially inwardly projecting shoulder therein, said rod terminating at both ends within said elongated members and having an enlarged head normally disposed in abutting engagement with said shoulder, and spring means mounted on said elongated members and cngaged with said heads in position to normally yieidingly hold said elongated members in said spaced relation to each other.

2. An overload unit as defined in claim 1 and in which said spring meaus comprises a compression spring comprising a stack of annular-shaped disc springs encircling said elongated members between said heads thereof.

References Cited in the file of this patent 7 UNITED STATES PATENTS 2,485009 Muller Oct. 18, 1949 2,522451 Johansen Sept. 12, 1950 2636,433 Wennberg Apr. 28. 1953 2.812,843 Hummel Nov. 12, 1957 FOREIGN PATENTS 497,752 France Sept. 24, 1919 

